Abstract: On a focus adjusting apparatus of an optical pickup apparatus, light reflected by a recording medium is concentrated into two focuses by an optical divider. First and second optical detectors are disposed so that a focus adjusting mechanism is controlled in accordance with the output of both detectors. Each optical detector includes central and peripheral light receiving planes. In a first system, the focus adjusting mechanism is controlled so that a difference of a ratio of a quantity of received light of the central light receiving plane to the whole quantity of received light of both the central and peripheral light receiving planes of the first optical detector and the same ratio of the second optical detector is reduced to O. Even if unblance occurs in the quantities of incident light to both the optical detectors, the unbalanced component is canceled between a denominator and a numerator of the above noted ratio.

Abstract: An optical recording head for use with a magneto optical recording device wherein a rhomboid prism is utilized having a single PBS coating thereon and being totally internally reflective so that light from a source will pass through the PBS coating once, be totally internally reflected, pass through the PBS coating a second time to form first and second beams, the first passing to the recording apparatus and the second being reflected to pass to a detector to monitor the intensity of the radiation. Light from the recording apparatus containing information is reflected back through the PBS coating to form third and fourth beams, the third being reflected to suitable detecting means and the fourth being passed through the rhomboid prism where it is internally totally reflected and emerges to a detector which is used for monitoring the focal position of the objective lens.